Microarrays, also known as biochips, have recently become important in the study of genomics. The use of a microarray involves laying down an ordered array of genetic elements onto a solid substrate such as a slide. Depending on the application, a microarray may consist of genomic DNA, reverse-transcribed cDNA, or smaller chains of oligonucleotides as well as any preparatory substrates. The microarray is useful because it allows genetic analysis to take place on a massively parallel scale, wherein thousands of genes and markers can be scored in one experiment.
A microarrayer, also known as a DNA array printer, is a high-capacity system used to print a microarray onto slides. Typically, a microarrayer is a specially built robotic platform designed to transfer solutions from the well of some type of microplate onto another surface for analysis. This process of depositing the liquid spot onto the slide is known as “spotting”.
Recently, microarrayers have become extremely popular in laboratories because they add to the efficient productivity of the laboratory to be able to print samples onto slides accurately and rapidly. Affymetrix, Inc., with offices in Santa Clara, California, makes an automated arrayer called the 417 ARRAYER (Part No. 0-0001 and Part No. 0-0009). BioRobotics, with offices in Boston, Massachusetts, produces two versions of an automated arrayer called the MICROGRID and MICROGRID II. GeneMachines, with offices in Menlo Park, Calif. makes an arrayer called the OMNIGRID (Model No. OGR-02). Packard Instrument Company with offices in Meriden, Conn. makes an automated arrayer called the BIOCHIP ARRAYER.
Although there are some differences between each of the above listed microarrayers, they are all similar in that they each spot microarrays in an automated fashion. However, there are significant problems with the prior art devices that detracts from their efficient operation.
A first problem arises due to the fact that as blank slides are cycled through prior art microarrayers, they can become askew or positioned improperly underneath dispensing tips. This problem results in spots being positioned improperly on the slides. A second problem can arise even if the slide is positioned correctly under the dispensing tips. It is possible for the spot to be deposited in the correct position, but be of poor quality and therefore useless as far as experimentation purposes.
Up to now, the only way to deal with these problems was to have a human operator visually monitor and inspect the microarrayer during its operation or inspect the samples after they come off the machine. This solution is an unacceptable waste of human effort. The BIOCHIP ARRAYER made by Packard Instrument Company has attempted to deal with the problem of monitoring the spotting process. However, it has only limited verification functionality with its integrated camera. This means that it verifies whether or not a spot has been dispensed, without any quality inspection to analyze whether that spot was good or bad.
What is needed is a better microarrayer with automated quality inspection capability.